This invention relates to feed-water heaters for steam power plants.
In steam power plants, a supply of steam at high pressure and high temperature flows through a steam turbine to drive the turbine as the steam expands. At an intermediate stage in the turbine, steam is bled from the turbine and conducted in- one or more feed-water heaters to heat the water that is finally supplied to the boiler, thereby increasing the efficiency of the system. A conventional feed-water heater includes a housing surrounding a heat exchanger. The feed-water for the boiler flows through a number of heat exchangers, and steam bled from the turbine flows into the housing to heat the water flowing through the heat exchangers.
If the feed-water heater housing is under vacuum during operation, a certain amount of atmospheric air will enter the pipeline system and as a result will enter the heater. In order to avoid having the noncondensable gases interfere with the transfer of heat between the heat exchanger surface and the steam, the noncondensable gases must be removed from the heater. The noncondensable gases remain stagnant around the heat exchanger surface, and reduce the thermodynamic efficiency of the feed-water heater. The accumulation of large quantities of noncondensable gases can also lead to severe corrosion of the heat exchanger tubing, especially if the chemical composition favors corrosion, such as ammonia contained in air.
Various proposals have been made for removing the noncondensable gases. It has been proposed, for example, to install baffles in the feed-water heaters to provide the proper flow of ths steam that is to be condensed. At the end of the condensation path, the noncondensable gases are then removed by suction devices. An example of such a system is disclosed in Mitteilungen der VGB, Number 102, June 1966, pages 184 to 190. These prior proposals have the main disadvantage that relatively high steam pressure losses, i.e. thermodynamic losses, will occur. This is especially true in the case of high output units because the distance between the individual baffles must be relatively close.
It is an object of this invention to design a feed-water heater which avoids the disadvantages of the prior and which will make it possible to remove the noncondensable gases efficiently from the feed-water heater.